The computer cursor is one of the most well known features of a computer display. Typically, the cursor is placed over a symbol of a program feature on the display and a switch associated with the cursor is activated to select the feature.
A number of different control devices have been developed to control the movement of the cursor. Examples include touch panels, joysticks or the computer mouse.
Touch panels and joysticks are typically located on the keyboard of a computer terminal while a computer mouse is separate from the keyboard and is, instead, directly connected to the CPU. In the IBM Thinkpad, the cursor switch is located directly below the space bar with the touch panel located below the cursor switch. In contrast, the joystick is surrounded on the keyboard by the letters g, b and h.
Since the joystick is surrounded by keys on a keyboard, the user must be careful not to activate any inappropriate nearby keys when the joystick is used. While the touch panel is somewhat easier to use, the cursor can only be moved a limited distance for each movement of a user's finger across the touch panel.
In contrast, a computer mouse can be placed in any location near the user. Since the mouse is separate from the keyboard, it can be more easily used without fear of activating the wrong key and without the distance limitations of a touch panel.
In order to move the cursor, internal circuitry of the mouse detects movement of the mouse across a supporting surface and translates that movement into cursor movement. In older devices, movement of the mouse is detected via a ball located inside the mouse. A set of encoder wheels placed ninety degrees apart make contact with the ball, thereby detecting movement of the ball and generating the signals controlling the x and y movement of the cursor. The encoders connected to the encoder wheels generate a pair of quadrature signals that is used to detect a direction of movement of the mouse.
In more recent devices, movement of an optical mouse is detected by moving the mouse over a control surface having a grid printed on the control surface. One or more light sources are provided within the mouse to direct light onto the grid. Reflected light from the grid is directed onto photodetectors within the optical mouse to detect movement of the mouse over the grid. By placing the photdetectors a predetermined distance apart, quadrature signals can again be provided as an indication of direction.
While the light sources and photodetectors of optical mice are a significant improvement over the use of a ball within the mouse, conventional light sources and photodectors are unnecessarily complex and inefficient. Because of the importance of computer mice, a need exists for means for detecting movement that are less complex and more efficient.